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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Posted on 28 May 2010 by John Cook

I don't plan to fall into the trap of breathlessly reporting every twist and turn of short-term climate fluctuations (I went through a bit of a silly period in March and April 2008). But we've been discussing Greenland trends and as it's been over a year since posting GRACE data on Greenland ice mass so I figure we're due an update. Many thanks to Tenney Naumer of Climate Change: The Next Generation who emailed me the graph. Thanks also to John Wahr at the University of Colorado who analysed the GRACE data and granted permission to reproduce it here. Figure 1 below shows the latest satellite gravity measurements of the Greenland ice mass, through to February 2010

This graph includes 12 months more data than Velicogna 2009 and shows the rate of ice mass loss is still increasing. Of course, this is only over an 8 year period. You get a broader picture when you combine GRACE data with other estimates of Greenland mass balance. Figure 2 combines altimetry, net accumulation/loss, GRACE gravity data. It doesn't include GPS measurement although this is consistent with other results, also showing acceleration in recent years.

Figure 2: Rate of ice loss from Greenland. Vertical lines indicate uncertainty, horizontal lines indicate averaging time. Blue circles are from altimetry, red squares are from net accumulation/loss and green triangles are from GRACE. The black line is a straight-line (constant acceleration) fit through the mass balance data for the period 1996–2008 with a slope of 21 gigatonnes/yr2 (Jiang 2010).

What we find is over a longer time period, Greenland was in approximate mass balance in the early 1990s. Before then, data is sparse but may have been slightly increasing in mass during the mid-20th century.

Comments

I don't suppose John Wahr wants the bother of monthly updating this data online. Near realtime updates of climate data are exciting.

(wait did I say exciting!)

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Response: Then I would be tempted to do regular blog posts on every twist and turn. I've been monitoring Roy Spencer's near-daily satellite data on surface temperature with great interest. To my credit, I've resisted the temptation to blog on it, wary of the fickleness of short-term fluctuations.

So perhaps we can take it as read that Greenland's got an accelerating mass deficit? That way-- in the upcoming inevitable discussion of why/how this has nothing to do with anthropogenic climate change-- we won't have to sift through a mass of previously failed "it's not shrinking/it's actually growing" hypotheses and stick w/somewhat more plausible alternate mechanisms not involving anthropogenic climate change. And how about those alternate ideas being posted here fully fleshed-out, with details of how they -ought- to work and then some confirmatory observations? Something remotely comparable to what John presents? That would be a really pleasant improvement.

(Sorry, somewhat out-of-patience here having listened for the past 24+ hours to BP's rapidly alternating stories about their oil leak while watching the video of the leak itself somehow remaining completely identical in appearance while it supposedly had tens of thousands of barrels of barite mud pumped into it, lost, shut off, then turned on again. I believe the mud's gone in, I guess, maybe, but I don't believe they had the well under control for any period of time.)

I'm not quite convinced by the last claim that there may have been a slight increase during the mid-20th century. Maybe you'd better say it the data doesn't exclude it?

If you like to update such plots with recent historical data.. it would be great to have one collection of important history plots of various quantities, updated whenever new data comes available. You could even try to get the scales to match, so the plots line up so correlations between the histograms can be seen.

.. and yes: very nice to get preliminary data plotted here! I guess we should also accept the reality that those preliminary points might still change a bit, e.g. if some calibration of measurement data changes. If the status of the most recent points is as preliminary as I'm guessing.. maybe it is a good idea to give them a different color or symbol. That way, if they change in the future, nobody can blow that up to another pseudo-scandal-gate.

“Some of the more optimistic emission scenarios from the IPCC predict warming of 1 to 2°C. The last time temperatures were this high were 125,000 years ago. At this time, sea levels were over 6 metres higher than current levels (Kopp 2009).”

2. It’s highly probably that even during the last 3,000 years there have been periods as warm as 1-2c greater than today without 6 metre increases in sea levels. That’s why it’s called Green Land. Melting around the coast and at low altitude is not unprecedented. Evidence for a Minoan Warm period of 3c warmer than today exists.

3. Even if true, why aren’t sea levels already much higher and rising faster than they are today? After all, it’s already warmed by at least .75c since 1900 that’s almost a third of the way there to 6 metre increases in sea level, but sea levels are only rising at 2-3mm a year. No consilience there.

4. The speed of current warming is also well within Holocene natural amplitudes. Both the Younger Dryas and The Akkadian Collapse occurred at rates that would have reduced modern civilization to rubble in a matter of years. In comparison today’s rate of warming is indeed mild. Although, that GRACE graphic is really scary looking!

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Response:"6 metre sea level rise is way beyond what IPCC scenarios suggest will occur at +1 to 2c temp rise"

Those IPCC predictions are for sea level rise by 2100. If you look at sea level prediction graphs, you'll note that sea levels are still rising sharply at that point. While you or I will probably not see beyond 2100, our grandchildren probably will. So there will be significant sea level rise beyond 2100 - it's just that the IPCC predictions don't go any further (to my knowledge). The timeframe of Kopp's 6 metre sea level rise is uncertain although other work indicates a timeframe of several centuries.

"Why aren’t sea levels already much higher and rising faster than they are today? After all, it’s already warmed by at least .75c since 1900 that’s almost a third of the way there to 6 metre increases in sea level"

The ice sheets have a great inertia - it takes a while for them to respond to the warming temperatures. In that sense, their great inertia is our friend. However, once they start disintegrating, it's not like we can throw a rope around the ice sheets and hold them back. At that point, the inertia becomes our enemy.

1. Yes, you are correct about what the IPCC said, but the statement by Kopp is also correct. If I remember their paper, 125,000 years ago temps were sustained at a level 1-2C higher than today, and sea level was about 6 meters higher.

2. "periods as warm as 1-2c greater than today without 6 metre increases in sea levels"

First, how long is a "period", because it matters. If you mean years, then very likely there has been a year in the last 3000 years 1-2C warmer than this year. But a year is too short to matter (or measure in the paleo-record). Decade? Also too short to matter as far as sea level goes, and still too short to measure in the paleo-record. Centuries? Now measurable in the paleo-record, and more likely to matter for sea level but less likley to be true.

On both 1 and 2, I think the time over which temperatures remain warm clearly matters.

3&4. Good questions, but when you look at where the sea level rise comes from, it takes time unless you are having a massive ice sheet or two collapse. So your comparison is certainly true but not very useful, I think, because the first 10-15,000 years after Last Glacial Maximum were a very different situation than anything since sea level roughly stabilized about 6000 years ago.

This means that your graphic of 2009 ice loss is out of date. According to the abstract of Velicogna 2009, the value of 286 Gt/yr was actually for 2007-2009 (and the data only went up to February 2009). From eyeballing the updated graph above, Greenland actually lost nearly 350 gigatonnes in 2009.

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Response: You people insist on creating work for me, don't you? I've upgraded the Greenland losing ice graph although now that I look at it, the content on that page needs a dramatic overhaul in light of recent posts. Sigh, damn advancing scientific knowledge...

Though this graph looks worrisome, the grand question remains if the rate will continue (to accelerate). It's not well understood how ice sheets loose mass, and what mechanism has caused the more rapid mass loss. Glaciers have rapid advancements and retreats, and it might be that ice sheets have somewhat identical melting patterns. I wouldn't count on it though. Still, I believe currently it is thought that it will take thousands of years before (if) the Greenland ice sheet melts completely.

The main uncertainty to be resolved is time frame. The latest research indicates roughly 1 to 2 metres sea level rise by 2100 but it's difficult to say how quickly sea level rise will evolve after that. However, this uncertainty does not serve as a basis for inaction - quite the contrary.

Arjan writes: Though this graph looks worrisome, the grand question remains if the rate will continue (to accelerate). It's not well understood how ice sheets loose mass, and what mechanism has caused the more rapid mass loss.

And Doug is right that it's not really useful to say "Well, it would take a long time for the entire Greenland ice sheet to disappear." A loss of 10% of the ice would leave Greenland looking superficially more or less similar to its present appearance -- but it would add 65 cm to sea levels worldwide, which, combined with thermal expansion and contributions from Antarctica and mountain glaciers, would probably mean more than a meter of sea level rise. That's very problematic.

You're right that the real question is if (or, more realistically, how much) the current loss of ice will accelerate over the next few decades. If global warming stopped now and the rate of loss stayed at a constant 200-300 GT/year, it would take a very long time to send 10% of that ice into the ocean. In the more probable case where the planet continues to warm and the rate of ice loss continues to accelerate, this could happen at the century time scale.

It has been said that, as Greenland ice melts, the landmass (relieved of this weight) will rise. If this is so, it should have an offsetting effect to the rising sea levels due to ice melt. If this is so, will the effect largely offset sea level rise from the melt water, or will it be insignificant?

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Response: The rising land is sharpest in regions where ice sheets are melting and yes, will offset sea level rise to some degree (perhaps even exceed it in some places). The effect is much less in other parts of the world. So as I explain in Greenland rising faster as ice loss accelerates, unless you have a huge melting ice sheet in your neighbourhood, you're unlikely to see uplift rates like those seen in Greenland.

#15 daisym, Greenland will rise faster than sea level rise if it continues to lose mass rapidly. This is currently happening in Alaska and Patagonia, where uplift due to rapid ice loss is several times faster than sea level rise. However, outside of the areas that are losing ice, land level won't change much and most of the world will just experience sea level rise.

Wes George, I do wish people would stop repeating unfounded myths as fact. First of all: Like today, Greenland during the MWP has always been an extremely marginal region for human settlement. I've seen nothing in historical records or paleoclimatic data to suggest that Greenland has *ever* been warmer-during the last 12,000 years-than it is today. The name Greenland was just an attempt by Eric the Red to encourage colonists to move there-it was not supposed to be an honest indication of what the place was like (though it did, & still does, get quite green around the coast during Summer).
As to the claims of temperatures more than 1-3 degrees warmer than today I say-cite your source! I've looked at numerous reconstructions, dating back as far as the end of the last glacial period, & the only time period that was apparently warmer than today was the so-called Climatic Optimum-around 12,000 to 8,000 years BP. Temperatures then were around 0.3 to 0.4 degrees warmer than the 20th C average (depending on which reconstruction you look at), but occurred over a period of *centuries*, not decades as is occurring now. Maybe the Mediterranean region was 3 degrees warmer during the Minoan period, than the *global* average today-but that's a purely *local* phenomenon & has no bearing on what global temperatures were like at that time (indeed, IIRC, much of North America & Northern Europe was very cold at this point in history-due to a slowdown in the Gulf Stream).

Well, I guess that's more likely than a total melt by 2065 for a 7 metre rise, something that was once suggested here as an admittedly remote possibility once.

Still, the IPCC models projected for even the worst possible scenario shows less than 50cm sea level rise by 2100 and only 100cm rise by 2200 and that's the worst case scenario...perhaps more likely 20 to 30cm by 2100. Big margin there.

2 metre rise scenario isn't until 2330 or so.

So, I guess your interpretation of the latest data disagrees with the IPCC worst possible scenario by a factor of 2 to 4?

Since the mass balance of a glacier is recorded on an annual basis, monthly or more frequent updates just do not make sense. Given the rapid snow melt off and well above average temperatures for Western Greenland this year, expect more losses.

Wes, the myth that you're repeating is this idea that-because it might have been warmer in one region of the world than global temperatures today-that this means we have nothing to worry about. There is evidence that Greenland was-at the *peak* of the MWP-as warm as temperatures are today (based on 18-O isotope levels in the ice), but this says nothing about the temperature in the rest of the Northern Hemisphere. What also needs to be remembered is that all the evidence suggests that the warm period that gave rise to the Greenland colony occurred over the space to more than 4 centuries-wheras the warming of the late 20th century has occurred in the space of barely 4 decades. Its highly probable that a more rapid *rate* of warming might have different impacts on Greenland's ice than all previous examples of relatively slow warming in the past.

John, what's the baseline for the ice mass anomalies? I looked for this in Velicogna 2009 but maybe missed it.

Meanwhile AMSU-A is still looking scary. I was rash enough to blog about it in April and it's still not disappointing. The thing is, we aren't meant to obsess about short-term changes because natural variability will overwhelm the long-term trend if we look at too short a period, but natural variability should be pushing temperatures down not up over this period.

wes george@18 I saw a Documentary on people living in siberia where to bury their dead they melted the permafrost with fire so they could dig a hole , they had to take turns working outside of 15 mins becuase it was so cold , maybe this is what the vikings did ?

Daved Green: Most ancient people of Siberia buried their dead in mounds above ground. The Viking graves were buried in the church yard in their settlement which couldn't have been permafrost because they were dairy farmers.

In post # 18 I tried to introduce evidence that the MWP was global in extent and as warm or warmer than today but it got snipped out by our moderator....

So I am reduced to saying only that because there is evidence that the MWP was as warm or warmer than today and no "tipping" point was reach causing the icecap to slip away as some have suggested it might, there is no reason to believe that it will do so today, other than a 7-year long scary-looking graphic in the 20,000 year history of the Greenland icecap.

My own bias here is towards the conception of the Greenland icecap as a relatively robust interglacial feature of the Earth's geophysiology. If it were so susceptible to succumb to temp perturbations only very slightly higher than today it's unlikely to have survived the last 8,000 years so intact.

Wes, do you think we might agree that the Greenland icecap is not "relatively robust" in the sense that a human artifact with purposeful over-engineering built into its design is robust?

Put another way, what leads you to believe Greenland's ice is so robust as to be unresponsive to small changes in its environment and controls?

I suggest instead that all the actual evidence we've been shown-- are indeed recording now-- indicates that ice on Greenland is quite responsive to its surrounding conditions, does not in fact have any degree of "robustness" at all. The ice sheet is no larger or smaller than it must necessarily be in the context of its surroundings.

Greenland's ice is not an engineered object. It is an emergent feature of its environment. What would be entirely surprising would be to find that as such it is somehow decoupled from its external conditions.

Marcus # 25, contends that modern warming is occurring at an anomalously rapid rate. I understand there must be a bias toward gradualism in the climate sciences, but recent studies seem to indicate many instances of extremely violent climate change has occurred in the past. Best known of these being the onset and decline of the Younger Dryas and the so-called Akkadian Collapse both of which appear to have achieved their full amplitude in a matter of years rather than decades. I would also dispute Marcus's characterization of the onset of the MWP as gradualistic or any of the other recent warm or cooling periods. Most recent climate phase shifts occurred at rates exceeding .5c a decade. Again, the paleoclimate reconstructions favored by some in the community perhaps don't reflect the full extent of volatility of recent past climate change.

As Marcus points out concern for a catastrophic collapse of Greenland's ice sheet is based primarily upon the assumption that modern warming is anomalous, indeed unprecedented in the Holocene. This is a testable assumption.

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Response:"concern for a catastrophic collapse of Greenland's ice sheet is based primarily upon the assumption that modern warming is anomalous"

I don't get this sense in the peer-reviewed literature. The concern for collapse of Greenland's ice sheet comes from the fact that when the Earth was 1 to 2 degrees warmer than now, sea levels were at least 6 metres higher than now. These higher sea level weren't because temperatures changed quickly during the last interglacial 125,000 years ago but due to sustained warmer temperatures.

Wes, I fail to see how the examples you're referring to address multiple lines of evidence indicating that Greenland's ice is shrinking at a rate that will combine with other contributors to exacerbate a developing problem w/sea level rise, now, when we're around to be affected by the result.

How do you draw the conclusion that our concern for ice loss on Greenland is based on the fact that modern warming is anomalous? For most of us the issue is that the ice is in fact melting, which is not an assumption.

Hmm. Younger dryas - I agree that the evidence points to the onset of COOLING as being very rapid. Also worth noting that younger dryas/Heinlich events would appear to be a feature of record only in times when moving out of glaciation.

"Akkadian Collapse" - I know little about this but isnt this sudden onset of drought? What evidence that this was a global event rather than regional? I would take very little comfort from this or other records of regional disruption of the hydrological cycle. Rapid change from whatever reason is difficult to adapt to and the fact the AGW predicts more disruptions like this in various parts of the worlds is worrying.

One other detail, you might like to look at the greenland past temperatures in Gareth's little graph for a perspective.

The real issue is that unlike past natural variations, we expect warming to continue or even accelerate unless we reverse changes to atmospheric composition. It is what happens to this in future that will determine the fate of greenland ice sheet.

Why would one cite evidence from 125,000 years ago, an entirely different era than the holocene?

Why not look at more recent warming, say like in the last 4,000 years? In the recent era surely many variables would be more tightly coupled to today than data from 125,000 years ago and have a higher resolution. Sure, there are no periods of recent past warming above today's temperature longer than a few centuries, perhaps even less. But our concern is melting over the next few decades rather than millennia.

Why indeed look back 125,000? Because of the assumption that no recent past record of warming 1c to 2c higher than today exists. No? Certainly, Greenland didn’t melt much during recent warm periods. Ie, concern for a catastrophic collapse of Greenland's ice sheet is based primarily upon the assumption that modern warming is anomalous, indeed, unprecedented in the Holocene.

So we got to go back 125,000 years to find a period where the sea-level was 6 plus meters higher than today? I find that an argument for the relative robustness of Greenland’s icecap rather than evidence that a 100,000 year old feature is likely to disappear rapidly due to a 1c to 2c temperature rise.

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Response: Why look back 125,000 years? You answered your own question - it's the most recent time when global temperatures were 1 to 2 degrees warmer than now.

Greenland didn't disappear 100,000 years ago - it's been around for at least half a million years. Using very rough back-of-the-napkin calculations, 6 metres sea level rise would receive perhaps 3 metres sea level rise from Greenland which would be less than half of the ice mass currently on the ice sheet. This is very roughly speaking, I'm not aware of the relative contributions from Antarctica versus Greenland.

The issue here isn't the total disintegration of Greenland (at least I hope it doesn't come to that). But even a partial collapse of the Greenland ice sheet will impose sea level rise in the order of metres plus a corresponding sea level rise from Antarctica (throw in melting glaciers and thermal expansion for good measure).

Why not look at more recent warming, say like in the last 4,000 years?

How about going one better, and looking at the warming happening now? Warming, ice melting. What could be simpler?

Wes, the ice sheet is melting right now, responding to a change in regime. What we know of the cause for that change suggests it's going to last for a long time.

As John and others have mentioned, the issue is not that the ice sheet is going to vanish, not now and not in our great-grandchildren's time. That's not the salient issue so don't worry about it. Worry instead about how to arrest the decline we're seeing now.

OK, so now we concede that concern for a catastrophic collapse of Greenland's ice sheet is based primarily upon the assumption that modern warming is anomalous and indeed, unprecedented in the Holocene?

Fine. What we need are testable assumptions. Not strawmen.

Speaking of strawmen, I understand that the real concern is the possibility that about 7% of the ice might melt by say 2090 leading to a one meter rise in sea levels, even though the current melt rate in the graph above if it continues uninterrupted indicates a sea level rise of 1 metre around in around 800 years. We've been through all that and it leads back to the whole unprecedented, anomalous warming meme.

Because, if today's warming isn't anomalous and unprecedented then we could simply look at other warm periods in the recent holocene for guidance. Right?

Moreover, even if today's relatively ordinary rate of warming (0.8c per century) is 100% anthropocentrically induced we won't be 1-2c warmer before 2080 to 2150. Surely, you don't doubt that peak oil-which is forecasted for virtually tomorrow- combined with exponentially accelerating technological evolution won't have pushed us well past a hydrocarbon-based economy long before then?

Wes, you mention "catastrophic collapse" and then within a handful of words yourself concede that's not actually the issue. Thanks for the swift return to reality.

...even though the current melt rate in the graph above if it continues uninterrupted indicates a sea level rise of 1 metre around in around 800 years.

Did you notice, the graph John displayed is curved, in the wrong direction?

Surely, you don't doubt that peak oil-which is forecasted for virtually tomorrow- combined with exponentially accelerating technological evolution won't have pushed us well past a hydrocarbon-based economy long before then?

A moving goal post we can agree on, and upon which I've got my hopes pinned.

Wes, you mention "catastrophic collapse" and then within a handful of words yourself concede that's not actually the issue

I also mentioned that’s strawman. But now that you bring it up: There was a post on this site that suggested if these trends not only continued on this very short slope but accelerate exponential then Greenland’s icecap will be gone in 65 years! To be fair the post mentioned that was unlikely, but still thought the possibility was worth a mention. However, the post has been modified over the weekend. Down the memory hole! Anyway, that’s where I got the idea that someone here might possibly believe in the imminent failure of Greenland’s icecap....within our children's lifetime! Silly me.

Wes: However, the post has been modified over the weekend. Down the memory hole! Anyway, that’s where I got the idea that someone here might possibly believe in the imminent failure of Greenland’s icecap....within our children's lifetime! Silly me.

Wes, let me help you plug your memory hole. The post you refer to is this one, still plainly in sight. It's an elliptical reference to a rhetorically witty but unproductive analysis found on a website not overly concerned with useful science.

"OK, so now we concede that concern for a catastrophic collapse of Greenland's ice sheet is based primarily upon the assumption that modern warming is anomalous and indeed, unprecedented in the Holocene?"

No - but because business as usual scenarios will cause more warming into a system still out of equilibrium. On the other hand Gareth's little graph gives you a perspective on modern temperature compared to rest of Holocene for greenland.

I certainly hope you are right about peak oil etc. but looking into past for when atmosphere was last at 450ppm, then sea level was hell of lot higher suggesting a long way to equilibrium. For questions as too how fast sealevel CAN rise from all sources, then perhaps look at Vermeer & Rahmstorf 2009.

Wes George writes: There was a post on this site that suggested if these trends not only continued on this very short slope but accelerate exponential then Greenland’s icecap will be gone in 65 years!

As Doug Bostrom points out, the comment of mine that you're referring to is right here.

I thought the point was obvious -- extrapolating the past decade's accelerating rate of ice loss leads to a physically unrealistic result (all ice gone by 2075) and thus is unreasonable. There is no realistic process that could ablate that much ice from that physical setting in that short a time.

My second point was that even a much slower acceleration than we're seen over the past decade would still have disastrous results. A much slower acceleration might leave 90% of Greenland's ice still intact in 2100, but would also contribute to a greater than one meter rise in sea level when combined with thermal expansion and loss of ice from West Antarctica and alpine glaciers.

Sea level is one area where the IPCC forecasts have clearly been too cautious (see here and here).

Wes George writes: Moreover, even if today's relatively ordinary rate of warming (0.8c per century) is 100% anthropocentrically induced we won't be 1-2c warmer before 2080 to 2150.

Where do you get that "2080 to 2150" from? Pretty much all the emissions scenarios (except the obviously unrealistic "Year 2000 constant concentrations") give 1-2 C warming by the middle of this century. Don't make the mistake of just projecting forward the 0.8 C we've experienced so far -- even if we capped emissions right now (which isn't going to happen), the rate would increase beyond that 0.8C per century because of additional warming in the pipeline thanks to slow feedbacks.

wes george, your accusation that a post had "been modified over the weekend. Down the memory hole!", has been shown to be incorrect, as far as I can see. Therefore, I think it only fair that you should admit your mistake and take back the false insinuation you made against this site.

IMHO, it's the rigorous and even-handed enforcement of that policy that has kept this site readable while the number of visitors has skyrocketed over the past year.

I'm not bothered by wg's claim that my comment was deleted; I'm bothered that he completely misinterpreted it ("that’s where I got the idea that someone here might possibly believe in the imminent failure of Greenland’s icecap....within our children's lifetime! Silly me.")

Philipm, that's really well written article, accessible by your use of analogies but with lots of data. Nice job.

The matter you mention of folks taking comfort from upticks since 2007 truly baffles me; the briefest scrutiny of past years' data reveals a monotonous succession of similar dips and rises, overwhelmed by an equally monotonous but much large ongoing slump. Blind men groping an elephant comes to mind.

Thanks for the kind comments on my article. No doubt those who went over there to read it saw some of the contrarian comments.

Doug #46, I don't interrogate the reasons for people taking comfort from irrelevant short-term variation, I merely destroy their hopes (and mine: it would be great if they were right). Meanwhile AMSU-A continues showing 2010 to be anomalously warm, given short-term effects. Let's hope the straw-clutchers let go soon enough for us to take effective action.

I'm changing my focus to talking up clean energy because I am convinced most people arguing against the science don't really understand it and are motivated more by fear that the alternative is a collapse of industrial society.

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